This invention relates to the field of microbiological processes and, more particularly, to the microbial production of lower aliphatic carboxylic acids.
At the present time when worldwide demand for organic chemicals is at an all-time high but the usual sources for many of such products, i.e., petroleum and natural gas, are in everdwindling supply, considerable interest has been directed to other forms of carbon such as biomass, coal and shale as raw material for industrial organic syntheses. Many fermentations utilizing carbohydrate substrates have been proposed or developed for obtaining organic materials. While ethanol fermentation is especially notable in this regard, other organics, notably the lower aliphatic carboxylic acids such as acetic, propanoic and butyric acid, have been successfully obtained as products of microbial metabolism. U.S. Pat. No. 1,371,611 describes a process for obtaining formic, acetic and butyric acids by the microbial fermentation of marine algae or sea-weed, presumably, the carbohydrate matter therein. U.S. Pat. No. 1,625,732 describes a process for producing butyric acid from the fermentation of hydrolyzed cellulose employing garden soil bacilli as the fermenting organism. Lactic and acetic acids are obtained from the fermentation of hexoses and pentoses by a microorganism whose characteristics are described in U.S. Pat. No. 1,856,425. Acetic, propionic and butyric acids or salts of organic acids are prepared by the fermentation of carbohydrates employing Bacterium acidi propionici, an organism isolated from Swiss cheese, as described in U.S. Pat. No. 1,913,346. Butyric acid is obtained in the process of U.S. Pat. No. 1,951,250 by the action of butyric acid bacteria on distillers' slop. Lower aliphatic acids, in particular, acetic, propionic and butyric acids, are obtained by fermenting a carbohydrate mash with the bacterium whose characteristics are described in U.S. Pat. No. 2,549,765. Dewatered human waste is metabolically utilized by a microorganism from the genus of Butyribacterium under anaerobic conditions to produce carboxylic acids which are thereafter decarboxylated to hydrocarbons in accordance with the process decribed in U.S. Pat. No. 3,962,035.
Coal, too, has been extensively studied as a raw material source for organic chemicals due to its abundance in many regions of the world, particularly in the United States where it is estimated to constitute 69% of the total estimated recoverable resources of fossil fuel whereas petroleum and natural gas are only about 7%. Many proposals for utilizing coal as a feed source for the manufacture of a variety of organic chemicals are initially based upon the partial oxidation of coal to provide a gaseous mixture predominantly made up of carbon monoxide and hydrogen, e.g., so-called "synthesis gas" or "syngas". Recent developments have led to a variety of catalyzed reactions involving the conversion of syngas to alkanols, glycols, carboxylic acids, esters, aldehydes, ethers, etc. Thus, for example, syngas has been catalytically converted to methanol in accordance with the reaction: EQU CO+2H.sub.2 .fwdarw.CH.sub.3 OH
It has previously been recognized that a strain of Eubacterium limosum (synonomous with Butyribacterium rettgeri) can utilize methanol to provide acetic acid (Hamlett, et al., Bacteriol. Proceed. Amer. Soc. Mirobiol., p. 149 (1969)). However, it has not been previously known or recognized that Eubacterium limosum (ATCC 8486) can convert carbon monoxide or a mixture of hydrogen and carbon oxide as, for example, obtained from the gasification of coal, to lower aliphatic carboxylic acids and/or corresponding salts.